Journal Cover Composite Structures
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0263-8223
   Published by Elsevier Homepage  [3120 journals]
  • Geometrically nonlinear bending analysis of functionally graded beam with
           variable thickness by a meshless method
    • Abstract: Publication date: 1 April 2018
      Source:Composite Structures, Volume 189
      Author(s): Jun Lin, Jiao Li, Yanjin Guan, Guoqun Zhao, Hakim Naceur, Daniel Coutellier
      Geometrically nonlinear bending deformation of Functionally Graded Beams (FGBs) with variable thickness is simulated by a meshless Smoothed Hydrodynamic Particle (SPH) method. The material properties of FGB is assumed to be varied smoothly in the thickness according to exponent-law distribution. To prevent the mesh-distortion in element-based numerical method, meshless SPH method is adopted, where corrective smoothed particle method and total-Lagrangian formulation are employed to improve its precision and stability. To validate the present SPH method, several numerical examples are performed and compared to analytical and finite element solutions.

      PubDate: 2018-02-05T08:30:00Z
       
  • Mechanical behavior of damaged laminated composites plates and shells:
           Higher-order Shear Deformation Theories
    • Abstract: Publication date: 1 April 2018
      Source:Composite Structures, Volume 189
      Author(s): Francesco Tornabene, Nicholas Fantuzzi, Michele Bacciocchi, Erasmo Viola
      The paper aims to present a novel mathematical formulation for the modelling of damage. In particular, the decay of the mechanical properties of the elastic media is modeled by means of two-dimensional smooth functions, which are the Gaussian and the ellipse shaped ones. Various damaged configurations are obtained as concentrated variations of the elastic properties of the materials by setting properly the parameters that define the distributions at issue. This approach is employed to investigate the dynamic behavior of damaged plates and shells made of composite materials. In particular, a massive set of parametric studies is presented for this purpose. The results are obtained numerically by means of the Generalized Differential Quadrature (GDQ) method and are presented in terms of natural frequencies. Several Higher-order Shear Deformation Theories (HSDTs), which can include also the Murakami’s function to capture the so-called zig-zag effect, are used and compared.

      PubDate: 2018-02-05T08:30:00Z
       
  • Sandwich diffusion model for moisture absorption of flax/glass fiber
           reinforced hybrid composite
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Hang Yu, Chuwei Zhou
      Flax/glass fiber reinforced hybrid composites take up a high amount of moisture from humid environment due to hydrophilic nature of flax fibers. Some experimental works have been carried out to investigate the diffusion kinetic of these hybrid composites with different stacking sequences. However, few analytical efforts have been made to effectively describe their moisture diffusion behaviors thus far. In this paper, a sandwich diffusion model is established to predict the moisture absorption behavior of flax/glass hybrid composites with different stacking sequences. To deal with interface concentration problem across flax fiber layers and glass fiber layers, the continuous normalized concentration and mass-conserving condition are employed. Both finite element analysis and moisture absorption experiments are performed to validate the proposed model, and the results shows that good agreements are achieved.

      PubDate: 2018-02-05T08:30:00Z
       
  • Experimental investigation on the mechanical behaviour of 3D carbon/carbon
           composites under biaxial compression
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Chenghai Xu, Leying Song, Hanxing Zhu, Songhe Meng, Weihua Xie, Hua Jin
      The effects of complex state of stress on the compressive behaviour of 3D carbon/carbon composites are investigated by application of uniaxial and biaxial loadings using a specially developed Zwick cruciform testing facility. The shape of the biaxially loaded cruciform specimen is optimised to avoid premature fracture outside the gauge section. A semi-analytical method is proposed to determine the stress components in the gauge section of the biaxial specimen. The experimentally obtained failure stress relation, which traces an elliptical path in the principal stress space, can be well represented by the Tsai criterion with a stress interaction parameter of F12 = −0.85. Macro-fracture morphology and SEM micrographs are examined and the results show that the failure mechanisms of the composites vary with the loading ratio. The results also suggest that the biaxial stress interaction effect is represented by a domain in the biaxial specimen, which is characterised by torsion and bending fractures in the dislocated fibres between two adjacent Z yarns.

      PubDate: 2018-02-05T08:30:00Z
       
  • The second strain gradient functionally graded beam formulation
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): S.A. Momeni, M. Asghari
      A size-dependent formulation for the Euler-Bernoulli nano- and micro-beams made of functionally graded materials (FGMs) is presented. The formulation is developed on the basis of the second strain gradient theory (SSGT). This theory is a powerful non-classical continuum theory capable of capturing the small-scale effects in the mechanical behavior of small-scale structures. To drive the governing equations of motion along with the general form of boundary conditions, the Hamilton principle is utilized. Due to the inhomogeneity through the thickness of functionally graded beams, the two equations which govern the axial and flexural deformations are coupled. In two case studies with different boundary conditions, the system of coupled equations is analytically dealt with, and the size-dependent response of FG beams in free-vibration and static behavior is numerically investigated. This investigation shows a significant difference between results of SSG theory and other non-classical and classical theories for very thin beams.

      PubDate: 2018-02-05T08:30:00Z
       
  • Multiscale finite element modeling of sheet molding compound (SMC)
           composite structure based on stochastic mesostructure reconstruction
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Zhangxing Chen, Tianyu Huang, Yimin Shao, Yang Li, Hongyi Xu, Katherine Avery, Danielle Zeng, Wei Chen, Xuming Su
      Predicting the mechanical behavior of the chopped carbon fiber Sheet Molding Compound (SMC) due to spatial variations in local material properties is critical for the structural performance analysis but is computationally challenging. Such spatial variations are induced by the material flow in the compression molding process. In this work, a new multiscale SMC modeling framework and the associated computational techniques are developed to provide accurate and efficient predictions of SMC mechanical performance. The proposed multiscale modeling framework contains three modules. First, a stochastic algorithm for 3D chip-packing reconstruction is developed to efficiently generate the SMC mesoscale Representative Volume Element (RVE) model for Finite Element Analysis (FEA). A new fiber orientation tensor recovery function is embedded in the reconstruction algorithm to match reconstructions with the target characteristics of fiber orientation distribution. Second, a metamodeling module is established to improve the computational efficiency by creating the surrogates of mesoscale analyses. Third, the macroscale behaviors are predicted by an efficient multiscale model, in which the spatially varying material properties are obtained based on the local fiber orientation tensors. Our approach is validated through experiments at both meso- and macro-scales, such as tensile tests assisted by Digital Image Correlation (DIC) and mesostructure imaging.

      PubDate: 2018-02-05T08:30:00Z
       
  • X-ray computed tomography observation of multiple fiber fracture in
           unidirectional CFRP under tensile loading
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Wonjin Na, Dongil Kwon, Woong-Ryeol Yu
      We investigated the initiation and propagation of fiber fracture in unidirectional (UD) carbon fiber-reinforced composites (CFRPs). The statistical fiber breakage of CFRPs and multiple fiber fracture (the propagation of fiber breakage near the broken fiber) have been studied and observed in specimens after fracture. To date, however, this propagation phenomenon has been rarely observed directly, and investigations have depended mainly on prediction. This direct non-destructive evaluation of fiber fracture phenomenon was performed via X-ray computed tomography of UD CFRPs. Specimens were loaded under various stress levels and imaged at low voltage (20 keV). The fiber breakages were analyzed from these images, which revealed multiple fractures leading to large clusters of broken fibers. Quantitative analyses after image processing revealed a marked increase in the number of multiple fractures, meaning the number of broken fibers in a broken fiber cluster, near the final fracture. Finally, the trend in multiple fractures was compared with the predicted results, showing reasonable agreement.

      PubDate: 2018-02-05T08:30:00Z
       
  • Effect of the extreme conditions on the tensile impact strength of GFRP
           composites
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): P.N.B. Reis, M.A. Neto, A.M. Amaro
      During operational conditions, extreme environments combined with unexpected high loading rates can induce severe damages or, inclusively, premature fails. Therefore, this paper intends to study the effect of different hostile solutions on the longitudinal impact strength in order to establish design criterions. For this purpose, samples of GFRP composites were immersed into alkaline and acid solutions as well as distilled water. Variables like exposure time, temperature and concentration of the solution were analysed in detail. The effect of pre-damages was also studied for different pre-loads, where the severity of the damages introduced was quantified by acoustic emission. It was possible to conclude that, independently of the solution, the exposure time and temperature were determinant to decrease the tensile impact strength. Finally, the magnitude of the initial damage has a significant influence on the impact resistance.

      PubDate: 2018-02-05T08:30:00Z
       
  • The effect of buffer-layer on the steady-state energy release rate of a
           tunneling crack in a wind turbine blade joint
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Jeppe B. Jørgensen, Bent F. Sørensen, Casper Kildegaard
      The effect of a buffer-layer on the steady-state energy release rate of a tunneling crack in the adhesive layer of a wind turbine blade joint, loaded in tension, is investigated using a parametric 2D tri-material finite element model. The idea of embedding a buffer-layer in-between the adhesive and the basis glass fiber laminate to improve the existing joint design is novel, but the implications hereof need to be addressed. The results show that it is advantageous to embed a buffer-layer near the adhesive with controllable thickness- and stiffness properties in order to improve the joint design against propagation of tunneling cracks. However, for wind turbine blade relevant material combinations it is found more effective to reduce the thickness of the adhesive layer since the stiffness mismatch between the existing laminate and the adhesive is already high. The effect of material orthotropy was found to be relatively small for the blade relevant materials.

      PubDate: 2018-02-05T08:30:00Z
       
  • Polybenzimidazole (PBI) film coating for improved hypervelocity impact
           energy absorption for space applications
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Sarath Kumar Sathish Kumar, Edwin Antonio Jurado-Manriquez, YunHo Kim, Chunghyeon Choi, Abrar H. Baluch, Chun-Gon Kim
      This paper deals with how the use of Polybenzimidazole (PBI) as a film coating over conventional composite designs could help improve the hypervelocity impact ballistic performance of the system. PBI coated composite samples were studied for resistance to Low Earth Orbit environment conditions like high vacuum, thermal cycling, Atomic Oxygen and Ultraviolet Radiation in a simulation facility. It was observed that the PBI coated composites reduced mass loss and surface erosion compared to the non-coated samples after LEO exposure. Hypervelocity impact experiments were conducted on the PBI coated composites for impact velocities between 2.5 to 3 km/s. The experiments showed that the PBI film coating significantly increased the energy absorption of the composite system. The effect of thickness increase as a result of the film application on energy absorption was also found to be negligible confirming the effectiveness of PBI coating as a hypervelocity shield.

      PubDate: 2018-02-05T08:30:00Z
       
  • Experimental and analytical study of the fibre distribution in SFRC: A
           comparison between image processing and the inductive test
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): Shengli Zhang, Lin Liao, Shuizhou Song, Changsuo Zhang
      The effect of the steel fibre distribution on concrete is significant, studies regarding the distribution characteristics of steel fibre are of great significance for the application of steel fibre-reinforced concrete (SFRC). Based on different mechanical test results, this paper aims to propose a reliable analysis method for more efficient evaluation of steel fibre distribution by using image processing and the inductive test to do comparison analysis on the steel fibre distribution in different concrete specimens. Firstly, the results of image processing and inductive test of different type of SFRC cubic specimens was analysed to obtain the steel fibre distribution, and a formula for rapid calculation of fibre content was proposed. Then, the influence of steel fibre distribution on the mechanical properties of SFRC was analysed by combining double punch test and three-point bending test results. Finally, the high similarity of the spatial distribution of steel fibre is analysed by the inductive test and image processing, which are reflected by the phase coefficient, and the applicability of these two methods are compared and evaluated.

      PubDate: 2018-02-05T08:30:00Z
       
  • 3D thermomechanical buckling analysis of perforated annular sector plates
           with multiaxial material heterogeneities based on curved B-spline elements
           
    • Abstract: Publication date: 15 March 2018
      Source:Composite Structures, Volume 188
      Author(s): M. Shariyat, H. Behzad, A.R. Shaterzadeh
      In the present paper, thermomechanical buckling of perforated functionally graded annular sector plates under uniform temperature rises and radial, circumferential or biaxial mechanical loads are investigated. Furthermore, effects of the circular cutouts on the buckling strength and deformation pattern are studied. Influence of the heterogeneity of material of the FGM sector in radial, circumferential, and transverse directions on the thermomechanical buckling is investigated for plates without or with one or two holes. Governing equations are derived based on the 3D energy-based theory of elasticity and buckling occurrence is detected by Treftz instability criterion. A novel curved 3D B-splined C 2-continuous element is proposed to trace the inter-element variations of the displacements and stresses and model the geometric discontinuities (cutouts). A proper algorithm is also proposed to relate events of the original cylindrical coordinates to those of the natural coordinates and vice versa. Instead of using the common von Karman assumptions, the most general form of the strain tensor in curvilinear coordinates is used. Finally, effects of the sector dimensions, size and orientation of the cutout, heterogeneity direction, direction of the mechanical loads and the combination of the thermal and mechanical loads on the buckling loads and mode shapes are investigated.

      PubDate: 2018-02-05T08:30:00Z
       
  • Analysis of an array of flexoelectric layered nanobeams for vibration
           energy harvesting
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): K.F. Wang, B.L. Wang, S. Zeng
      Comparing with a single energy harvester, an array of energy harvesters can provide higher electrical power output and wider frequency bandwidth. In this article, with consideration of surface effect, an array of layer flexoelectric nanobeams with proof mass connected in parallel and/or series are investigated. Governing equations are derived based on the Hamiltonian principle. Reduced order models for both parallel and series systems are obtained. Closed-form expressions for voltages are presented. Results show that the power, the frequency and the optimal resistances of the system are dependent of surface effect. The flexoelectricity has more significant effect on the normalized power however its effect on the frequency and the optimal resistances can be ignored. The optimal resistance of the system depends on surface effect, the number of array elements and its circuits. Moreover, increasing proof mass delivers a wider bandwidth at the cost of peak normalized power. The peak normalized voltage and power of the parallel system is small than those of the series system, but the bandwidth of the two systems is the same. This is important information for the design of an array of flexoelectric energy harvesters.

      PubDate: 2018-02-05T08:30:00Z
       
  • A Bayesian framework for fatigue life prediction of composite laminates
           under co-existing matrix cracks and delamination
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Matteo Corbetta, Claudio Sbarufatti, Marco Giglio, Abhinav Saxena, Kai Goebel
      This paper proposes a particle filter-based Bayesian framework for damage prognosis of composite laminates exhibiting concurrent matrix cracks and delamination. Literature shows a number of applications of particle filtering for real-time prognosis of metallic structures and, recently, matrix crack density evolution in composites. The work presented here enhances the methodology proposed in previous papers by extending the Bayesian framework to multiple damage mechanisms, and validates the approach using damage progression data from notched cross-ply CFRP coupons subject to tension-tension fatigue. A multiple damage-mode model for the estimation of the strain energy release rate and the remaining stiffness of damaged laminates constitutes the core of the particle filtering algorithm, thus allowing the prognostic framework to extend for monitoring of simultaneous, coexisting damages. Also, the damage state can be evolved into the future enabling simulation of damage progression and prediction of remaining useful life of the composite material. The proposed prognostic unit successfully predicts damage growth and fatigue life of the laminate, and the results are critically discussed with respect to filtered estimation of damage progression and remaining life prediction.

      PubDate: 2018-02-05T08:30:00Z
       
  • An analytical scaling approach for low-velocity impact on composite
           structures
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Raffael Bogenfeld, Janko Kreikemeier, Tobias Wille
      For the analysis of low-velocity impact, this work provides an analytic scaling approach, permitting to analyze structural impact scenarios on a small reference coupon. Thus, the numerical prediction of impact damage on large structures through high-fidelity methods is made possible. Yet, the massive computational effort needed for these virtual tests even on a coupon level means a major challenge to their application in the design process of a structure. To reduce the computational effort, local analysis approaches consider only damage-prone areas for an actual damage analysis. Our approach permits the analysis of structural impact scenarios on a much smaller reference coupon that represents the damage-prone area. An analytical spring-mass model transfers the impact parameters between the structural and the coupon level. For this purpose, the spring-mass model captures the impact-damage state by a scalar parameter. The transfer between the reference coupon and the structure is based on the equivalence of this damage parameter. Thus, a coupon simulation or coupon test result is given validity for a structural impact scenario. So, based on a single coupon simulation, areal impact assessment of a structure is made possible. This methodology is validated through experiments and a demonstrated on a generic aircraft door structure.

      PubDate: 2018-02-05T08:30:00Z
       
  • The effects of bond, shrinkage and creep on cracking resistance of steel
           and GFRP RC members
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): R. Balevičius, M. Augonis
      The analytical and numerical models for combining the effects of bond, shrinkage, creep and ageing of concrete on the stress-strain state and cracking resistance of reinforced or prestressed concrete elements in a period prior to loading are proposed. A geometrical meaning of the coefficient of ageing is defined in terms of an average stress-strain approach. It is mathematically proven that this coefficient integrally establishes a continuous shape function of the actual concrete stress (or its increment) in a given period of time. This allows for substituting the rectangular stress diagram for the actual function of stress in time to attain the same areas of these diagrams and explicit predicting the stress-strain state in time by using algebraic equations for the inverse of Volterra integrals. The analytical formulae for predicting the cracking moment of the cross-section accounting for bond, shrinkage, creep and ageing of concrete are also proposed. It is demonstrated that the intense development of the partially recoverable instantaneous and creep strains play the main role. The proposed formulae are applicable to the assessment or retrofitting of the existing structures, where the full contact interaction techniques are inappropriate.

      PubDate: 2018-02-05T08:30:00Z
       
  • Homogenized and localized responses of coated magnetostrictive porous
           materials and structures
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Qiang Chen, Guannan Wang
      The homogenized properties and localized field distributions of coated magneto-strictive porous heterogeneous materials are extensively investigated using the extended Finite Volume Direct Averaging Micromechanics (FVDAM) with coupled mechanical-magnetic capabilities. Both square and hexagonal microstructures are employed to mimic different hollow coating arrangements. In order to validate the present technique, the corresponding finite element model is constructed in Abaqus to provide rigorous comparisons, and no visible difference is observed between two different models’ predictions. The effects of the thickness of coatings are tested on the effective and local responses, where the hollow coatings play significant roles in the variations of homogenized properties and transmissions of stress concentrations. Finally, a two-step multiscale framework is established on periodic wavy structures, wherein the layers are composed of CoFe2O4 material reinforced by BaTiO3 hollow coatings with two different volume fractions. The amplitude-to-wavelength ratio is varied to effectively study its impact on the field distributions of homogenized layers and local microstructures.

      PubDate: 2018-02-05T08:30:00Z
       
  • Anisotropic hyper-viscoelastic behaviors of fabric reinforced rubber
           composites
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Heng Yang, Xue-Feng Yao, Han Yan, Ya-nan Yuan, Yi-Feng Dong, Ying-Hua Liu
      In this paper, an anisotropic hyper-viscoelastic constitutive model considering the temperature effect for the reticulated fabric reinforced rubber composites is developed. First, the hyperelastic part presents the effects of fiber fabric and the interaction between the rubber and the fiber fabric; the viscoelastic part is described by Prony series functions, also the temperature effect on the mechanical response for the fabric reinforced rubber composites is considered in the hyper-viscoelastic constitutive model. Second, the material parameters of the constitutive model are determined by means of fitting the test results of the rubber and the fabric reinforced rubber composites. Finally, the proposed constitutive model is used to simulate the compression and the relaxation response of fabric rubber seal, which is in good agreement with the corresponding experimental results. The study will provide an effective model to characterize and predict the hyperelastic and viscoelastic behaviors of fabric reinforced rubber composites at different temperatures.

      PubDate: 2018-02-05T08:30:00Z
       
  • Complex dispersion relations and evanescent waves in periodic beams via
           the extended differential quadrature method
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Z.B. Cheng, Z.F. Shi, Y.L. Mo
      Because of computation difficulties, investigations about the complex band structures and the evanescent wave modes in phononic crystals are very limited. In this paper, a novel k ( ω ) method, referred to as the Extended Differential Quadrature Element Method (EDQEM), is successfully developed to investigate the complex dispersion relations and the evanescent wave modes in periodic beams. At first, based on the Bloch-Floquet theorem and the two widely used beam theories, i.e., the Euler-Bernoulli beam theory and the Timoshenko beam theory, the EDQEM is developed to solve the dispersion equations of flexural waves in periodic beams. Comparisons with other related investigations are conducted to validate the correctness of the proposed method. Furthermore, considering three important factors, the shape of the unit cell, the pattern of the sampling point as well as the number of the sampling point, the convergence of the proposed method is investigated. Second, with the help of the EDQEM, complex dispersion relations of periodic beams are investigated and wave mode analysis is conducted, from which all possible waves, including propagative waves, purely evanescent waves and complex waves, in the complex dispersion curves are discussed. It is found that complex wave modes in periodic beams arise from two situations: (1) at the boundary of the first Brillouin zone and (2) within the first Brillouin zone. These complex wave modes are the transition modes between two propagative waves, or between the propagative wave and the complex wave. When the damping effect is included, all waves in periodic beams transfer into the complex waves. And, band gaps are not truly apparent anymore.

      PubDate: 2018-02-05T08:30:00Z
       
  • Nonlinear elastodynamics of piezoelectric macro-fiber composites with
           interdigitated electrodes for resonant actuation
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): D. Tan, P. Yavarow, A. Erturk
      Macro-fiber composite (MFC) piezoelectric materials are used in a variety of applications employing the converse piezoelectric effect, ranging from morphing and bioinspired actuation to vibration control in flexible structures. Most of the existing literature to date considered linear material behavior for geometrically linear oscillations. However, in many applications, such as bioinspired locomotion using MFCs, material and geometric nonlinearities are pronounced and linear models fail to represent and predict the governing dynamics. The predominant types of nonlinearities manifested in resonant actuation of MFC cantilevers are piezoelectric softening, geometric hardening, and inertial softening. In the present work, we explore nonlinear actuation of MFC cantilevers and develop an experimentally validated mathematical framework for modeling and analysis. In the experimental setting, an in vacuo actuation scenario is considered for a broad range of voltage levels (from low to moderate values) while eliminating nonlinear fluid damping. Experiments are conducted for an MFC bimorph cantilever, and model simulations based on the method of harmonic balance are compared with experimental frequency response curves under resonant actuation. The resulting experimentally validated framework can be used for simulating the dynamics of MFCs under resonant actuation, as well as parameter identification and structural optimization for linear to moderately nonlinear regime.

      PubDate: 2018-02-05T08:30:00Z
       
  • Low-frequency sound radiation of infinite orthogonally rib-stiffened
           sandwich structure with periodic subwavelength arrays of shunted
           piezoelectric patches
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Zhifu Zhang, Shande Li, Qibai Huang
      In order to minimize the low-frequency sound radiation of an infinite orthogonally rib-stiffened sandwich structure, the periodic subwavelength arrays of shunted piezoelectric patches are introduced. Based on the piezoelectric shunt technique and effective medium method, the panels and piezoelectric patches are equivalent to two homogeneous facesheets. Then, considering all the inertia terms of the rib-stiffeners, a complete theoretical model is built for harmonic point force excitation by using Kirchhoff’s thin plate theory. The vibration displacements of the facesheets in wavenumber space are solved by Fourier transform technique to complete the prediction of vibroacoustic responses. Furthermore, the correctness and effectiveness of the present model are verified by sequentially using published analytical models, simulation results and theoretical predictions in strict accordance with two prerequisites. At last, the influence laws of key influencing parameters on the research structure are investigated. All the results demonstrate that the proposed structure can effectively attenuate the structural radiation.

      PubDate: 2018-02-05T08:30:00Z
       
  • Experimental study on compressive behavior and failure analysis of
           composite concrete confined by glass/epoxy ±55° filament wound pipes
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Lokman Gemi, Mehmet Alpaslan Köroğlu, Ashraf Ashour
      This paper investigates the strength and ductility of concrete confined by Glass/Epoxy ±55° Filament Wound Pipes (GFRP) under axial compression. A total of 24 cylindrical specimens were prepared with expansive and Portland cements, properly compacted and un-compacted for different composite fresh concrete matrix. Test results showed that compressive strength and axial deformation at failure of concrete confined with GFRP tubes increased by an average of 2.85 and 5.57 times these of unconfined concrete, respectively. Macro and micro analyses of GFRP pipes after failure were also investigated. Debonding, whitening, matrix/transfer cracking, delamination and splitting mechanisms were detected at failure, respectively. The experimental results were also employed to assess the reliability of design models available in the literature for confined concrete compressive strength.

      PubDate: 2018-02-05T08:30:00Z
       
  • Numerical failure assessment of multi-bolt FRP composite joints with
           varying sizes and preloads of bolts
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Bibekananda Mandal, Anupam Chakrabarti
      A three dimensional (3D) progressive damage model (PDM) is developed for the failure assessment of fibre reinforced plastic (FRP) composite bolted joints subjected to bolt preloads. Material constitutive equations and material damage model are defined in a user-subroutine UMAT which is integrated with the finite element (FE) software ABAQUS. Fibre and matrix failure in tension, compression or in shear along with delamination failure criteria are incorporated in the present numerical model. Load-displacement behavior, laminate surface strains, propagation of damage and failure of a double-lap multi-bolt composite joint have been studied and present results are validated with the results available in literature. Failure of double-lap multi-bolt FRP joints with different bolt diameters and bolt tightening torques have been investigated using the proposed progressive damage model.

      PubDate: 2018-02-05T08:30:00Z
       
  • Influence of a fiberglass layer on the lightning strike damage response of
           CFRP laminates in the dry and hygrothermal environments
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Yichao Li, Tao Xue, Renfu Li, Xianrong Huang, Lijian Zeng
      This paper experimentally investigates the lightning strike response of a fiberglass/carbon woven hybrid laminate ([(0/90)g(45/02/−452/902)c]s) under dry and hygrothermal conditions. Damage characteristics are evaluated using various inspection methods and possible damage mechanisms are discussed. Observations demonstrate that as the increase of lightning amplitude, notably enlarged carbon fiber breakage and fiberglass delamination areas as well as fiber bulging are presented in the in-plane and in-depth directions. Compared to a [452/02/−452/902]s carbon woven specimen, the carbon fiber damage area, internal delamination area and damage depth for the hybrid one are 4.94 times, 2.26 times, 3.21 times greater under 22 kA lightning strike and 3.34 times, 1.97 times, 1.67 times greater under 32 kA strike, respectively. Hygrothermal aging significantly intensifies lightning strike damage on the hybrid specimen with complete detachment of fiberglass layer and massive internal delamination. The possible mechanism for the present damage behavior is analyzed. These results suggest that the fiberglass layer is not expected to protect the integrity of the carbon fiber reinforced polymer structure from lightning strike damage.

      PubDate: 2018-02-05T08:30:00Z
       
  • Torsional strengthening of RC beams using NSM CFRP rope and innovative
           adhesives
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Ghaidak Al-Bayati, Riadh Al-Mahaidi, M. Javad Hashemi, Robin Kalfat
      The strength of reinforced concrete (RC) members can be increased by bonding carbon fibre-reinforced polymers (CFRP) using externally-bonded reinforcement (EBR) and near-surface mounted (NSM) techniques. However, to date few studies in the area of torsional strengthening have been performed using NSM methods. Although the efficacy of increasing the flexural and shear strength of RC beams has been well reported using the NSM technique bonded with epoxy resins, the poor performance of epoxy in high-temperature environments and toxic fumes have been motivating factors for using new cement-based adhesives as a replacement adhesive for epoxy in several studies. This paper investigates the torsional behaviour of RC beams strengthened using NSM FRP laminates and FRP ropes. An epoxy adhesive was used in four beams and a new cement-based adhesive was utilised in the remaining four beams and used to evaluate the torsional capacity. Both CFRP laminates and CFRP ropes were embedded into pre-cut grooves. According to the results, the torsional behaviour of the beams strengthened with CFRP ropes was superior to that of the beams strengthened with CFRP laminate when using epoxy resin and cement-based adhesive. Generally, the epoxy was more effective in increasing the torsional strength than the cement-based adhesive.

      PubDate: 2018-02-05T08:30:00Z
       
  • A modified Arcan test for mixed-mode loading of bolted joints in composite
           structures
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Garth M. Pearce, Congyuan Tao, Yong H.E. Quek, Nayeem T. Chowdhury
      A novel modified Arcan test rig has been developed for testing the combined loading performance of bolted joints in composite laminates. The fixture was designed to complement existing bearing test standards (ASTM D5961) and pull-through test standards (ASTM D7332) for fastened joints in composite laminates. The new mixed-mode loading fixture fills a crucial niche, as interaction between pull-through and bearing failure modes can potentially reduce the overall joint performance and lead to anti-conservative designs. The test fixture was benchmarked against ASTM standards and was found to reliably reproduce pull-through failure behaviour observed during D7332-B testing. The comparison with D5961-B was less favourable, but the test specimens and configurations differ considerably. Work is underway to benchmark the new rig against D5961-C, which is a more comparable specimen configuration. Two mixed-mode test programs are reported in which joints were loaded at mixed-mode ratios between pure bearing and pure pull-through. It was found that the ‘failure’ load was well predicted by a quadratic mode-mixing rule. Conversely, the ‘maximum’ joint load was considerably over-predicted by a quadratic mode-mixing rule which could lead to anti-conservative predictions, particularly for dynamic systems in which joint damage is considerable. Based on the success of the preliminary testing, there is a strong case for further development and benchmarking of the new test fixture. There is scope for this fixture to be added to the suite of accepted test standards for bolted joints in composite structures.

      PubDate: 2018-02-05T08:30:00Z
       
  • Predicting bond behavior of HB FRP strengthened concrete structures
           subjected to different confining effects
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Cheng Chen, Lili Sui, Feng Xing, Dawang Li, Yingwu Zhou, Pengda Li
      This paper presents an analytical model to predict the bond behavior of hybrid bonded (HB) fiber reinforced polymer (FRP) strengthened concrete structures considering different confining effects. The bond strength of HB-strengthened concrete structures subjected to uniaxial loading is attributed to the friction-type bond from steel plate and the chemical bond provided by epoxy-based resin. The friction-type bond is assumed to develop before any interfacial slip occurs, and remain constant when the interfacial slip is nonzero; for the chemical bond between FRP and concrete, a tri-linear bond-slip relation is adopted. The loading process of HB-strengthened structures consists of three stages, and the stage-wise solution to slip, bond stress, and axial force of HB FRP are derived based on a governing ordinary differential equation (ODE). In this study, the experimental program includes twelve HB-strengthened concrete specimens, using different confining effects (twisting moments on the steel bolts). Test results indicated that the ultimate pullout strength increases and the failure mode switches from debonding to FRP rupture as the twisting moment increases. Moreover, by comparison to three series of experimental results, the proposed model can precisely predict failure mode, ultimate strength, load-slip relation and bond stress distribution. The twisting moment on bolts is found to have the most significant improvement on the ultimate tensile strength. Finally, the critical twisting moment without yielding FRP rupture is derived.

      PubDate: 2018-02-05T08:30:00Z
       
  • A numerical approach for modeling response of fiber reinforced polymer
           strengthened concrete slabs exposed to fire
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): V.K.R. Kodur, P.P. Bhatt
      A numerical model for evaluating the performance of fiber-reinforced polymer (FRP) strengthened reinforced concrete (RC) slabs under fire conditions is presented. The numerical model utilizes a macroscopic finite element based approach to trace thermo-mechanical response of FRP-strengthened RC slabs from linear elastic stage to collapse under fire conditions. The model accounts for temperature dependent properties of concrete, steel, FRP, and fire insulation as well as for temperature induced degradation of bond between concrete and FRP. The model is validated by comparing predicted response of FRP strengthened RC slabs with measured temperatures and deflections in fire tests. A case study is also presented to compare fire performance of RC slabs with and without FRP strengthening, as well as with different insulation and bond configurations. Results from the analysis indicate that a FRP strengthened RC slab, without any fire insulation, yields lower fire resistance as compared to conventional RC slab. Also, temperature induced bond degradation significantly influences fire performance of an FRP strengthened RC slab and neglecting bond degradation may lead to un-conservative estimation of fire resistance.

      PubDate: 2018-02-05T08:30:00Z
       
  • Nonlinear dynamic and deployment analysis of clustered tensegrity
           structures using a positional formulation FEM
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Ziyun Kan, Haijun Peng, Biaoshong Chen, Wanxie Zhong
      This paper addresses the dynamic analysis of the clustered tensegrity structures via the framework of the positional formulation finite element method (FEM). The nodal coordinates are chosen as the generalized coordinates. The rod element and multi-nodes clustered cable element are first formulated. A comprehensive dynamic model for investigating the dynamic properties of the clustered tensegrity is then developed. The dynamic model is subsequently modified for the structural vibration analysis and modal analysis. The results of the modal analysis show that each order of natural frequency of a clustered tensegrity is lower than that of its corresponding classical tensegrity, indicating that the structure tends to be more flexible if a classical tensegrity is transformed into a clustered tensegrity. The results of the nonlinear deployment analysis show that the motion characteristics differ from those of the quasi-static analysis as the actuation speed increases. To pursuit a fast actuation speed to actuate the structure, mere quasi-static analysis in the existing literature is inadequate, and dynamic effects must be taken into account. The proposed method provides an effective tool to capture the dynamic properties, such as the determination of an appropriate actuation speed, and to actuate the clustered tensegrity.

      PubDate: 2018-02-05T08:30:00Z
       
  • Hierarchical anisogrid stiffened composite panel subjected to blast
           loading: Equivalent theory
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Bei Zhang, Fengnian Jin, Zheng Zhao, Zhongxin Zhou, Ying Xu, Hailong Chen, Hualin Fan
      Hierarchical anisogrid stiffened panels (HASPs) have two-level stiffeners. The primary stiffeners improve the global stiffness of the HASP and the sub-stiffeners enhance the local stiffness of the mono-cell skin supported by the primary stiffeners. A smearing method was proposed to homogenize the HASP into a homogenous panel, based on two-step equivalences of extensional rigidities and bending rigidities. Dynamic responses of blast-loaded HASPs were analyzed based on the homogenous panel and the mode superposition method and validated by finite element (FE) analysis. Commonly the HASP vibrates like a homogenous panel and the theoretical prediction is accurate. Local mono-cell vibration appears only when the skin and the sub-stiffeners are weak enough. The model was applied to analyze the blast response of a composite protective door. Failure criterion based on maximum strain was proposed to predict the peak blast pressure the HASP can bear. The equivalent theory has good accuracy, providing a feasible way to analyze blast responses of HASPs.

      PubDate: 2018-02-05T08:30:00Z
       
  • Simulation of fire resistance behaviour of pultruded GFRP beams – Part
           I: Models description and kinematic issues
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): T. Morgado, N. Silvestre, J.R. Correia
      This two-part paper presents a numerical study about the fire resistance behaviour of pultruded GFRP profiles with square tubular cross-section subjected to bending and the ISO 834 time-temperature curve. The first paper deals with the development of numerical and analytical models and the discussion of relevant kinematic issues, including the evolution of beam deflection and position of neutral axis with the fire exposure time. The second part [1] reports an in-depth investigation on the side of static issues, which include the evolution of stress distributions and failure initiation with the fire exposure time. In the present paper, three–dimensional finite element models were developed to simulate fire resistance tests previously conducted by the authors on GFRP beams, in which different degradation curves were considered for compressive, tensile and shear moduli, based on experimental data. In these numerical simulations, both effects of varying the assignment of material properties (depending on the position of neutral axis) and of considering different thermal expansion coefficients were taken into account, and some conclusions were drawn on their influence on mid-span deflection evolutions. Since no failure criterion was implemented, both models were not able to reproduce the failure of the beams, but the overall tendency of the numerical results was consistent with the experimental data. Alongside the numerical study, analytical models based on Timoshenko beam theory were also developed and allowed obtaining accurate predictions of the mid-span deflection evolution of the GFRP beams; the analytical results were in close agreement with the numerical ones and also with the experimental data.

      PubDate: 2018-02-05T08:30:00Z
       
  • Analytical analysis of forced vibration of the hard-coating cylindrical
           shell with material nonlinearity and elastic constraint
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Yue Zhang, Wei Sun, Jian Yang, Qingkai Han
      In this paper, the nonlinear vibration characteristics of the hard-coating cylindrical shell with the base excitation and un-classical elastic constraint are investigated based on the Rayleigh-Ritz method. A continual variable stiffness elastic constraint is presented to introduce the actual uneven distribution of connection stiffness into the analytical vibration analysis. The nonlinear governing equations of motion are formulated by the Love’s first approximation theory and von Karman-type nonlinear strain-displacement relationship. The admissible displacement functions are constructed by the Gram-Schmidt orthogonal polynomials. To effectively consider the effects of the strain dependences of storage modulus and loss factor of hard coating on the vibration characteristics of the shell, a modified domain decomposition method is employed to determine the equivalent strain of hard coating under the action of base excitation. By extending the Newton-Raphson iterative scheme, a unified iterative solution method is developed for solving the nonlinear resonant frequencies and responses of the hard-coating cylindrical shell. The numerical and experimental examples of the cylindrical shell coated with NiCoCrAlY + YSZ are performed to validate the accuracy and reliability of the developed analytical model. The mechanism of soft nonlinearity displayed in the amplitude-frequency curves of the hard-coating cylindrical shell is discussed as well.

      PubDate: 2018-02-05T08:30:00Z
       
  • Dynamic instability of variable angle tow composite plates with
           delamination
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Xiaodong Chen, Guojun Nie, Zhangming Wu
      In this paper, the dynamic instability of variable angle tow (VAT) plates with a single rectangular delamination is studied using an analytical model. The analytical model is derived from the principle of potential energy based on the classical laminated plate theory. Both global and local behavior of delaminated VAT plates in the dynamic instability analysis are accurately captured by the use of multiple Legendre polynomial series. The equations for the motion in dynamic instability problem are derived using Hamilton’s principle. The dynamic instability regions are determined from the resulting Mathieu differential equations, which are solved using Bolotin’s approach. To validate the proposed analytical model, both critical buckling loads and natural frequencies of delaminated VAT plates are evaluated and compared with FEM results. The influence of delamination on the buckling load, natural frequency and dynamic instability region (DIR) of delaminated VAT plates is examined by numerical examples. A parametric study is subsequently carried out to analyze the effect of linearly varying fibre orientation angles on the dynamic instability response of delaminated VAT plates. Finally, the mechanism of applying variable angle tows to improve the dynamic stability performance of delaminated composite plates is studied.

      PubDate: 2018-02-05T08:30:00Z
       
  • Comparing the effect of geometry on the stress-strain response of isolated
           corrugation structures and corrugation reinforced composite structures
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Mark Fraser, Hatem S. Zurob, Peidong Wu
      The use of a corrugated geometry can improve necking strain without sacrificing strength when compared to similar structures with a straight geometry. In this work, Finite Element Modeling (FEM) simulations were performed exploring how the presence of a matrix material in a composite impacts the ability of the corrugated structure to improve the necking strain when compared to isolated corrugations with the same geometry. It was found that unlike for isolated corrugations, the degree of corrugation present in a corrugation reinforced composite must exceed a threshold value in order to overcome the improvement in ductility caused by the presence of the matrix. In addition it was shown that it is the unbending of the corrugation that leads to a boost in work hardening which ultimately postpones necking.

      PubDate: 2018-02-05T08:30:00Z
       
  • Effect of the manufacturing process on the energy absorption capability of
           GFRP crush structures
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): A. Esnaola, I. Tena, I. Saenz-Dominguez, J. Aurrekoetxea, I. Gallego, I. Ulacia
      Quasi-unidirectional E-glass/polyester semi-hexagonal composite structures manufactured by different processes (vacuum assisted infusion, hand lay-up and ultraviolet (UV) cured pultrusion) have been studied for automotive crash applications. In order to evaluate the effect of the manufacturing process in energy absorption capability of the material, the interlaminar shear strength (ILSS) and the specific energy absorption (SEA) capability of the material have been characterised. Hand lay-up and UV cured pultrusion samples have shown similar ILSS values, around 43 MPa. However, the ILSS of the infusion samples is 33 MPa due to the uneven distribution of the fibres along the thickness of the samples. Furthermore, the lower values of ILSS have resulted in the lowest SEA values for the infusion samples; 31 kJ/kg. Hand lay-up samples have shown the highest SEA values (52 kJ/kg) and UV pultrusion samples slightly lower (49 kJ/kg) values due to a higher void content. Nonetheless, the material manufactured continuously by UV curing pultrusion process has shown high energy absorbing capabilities for crashworthiness applications.

      PubDate: 2018-02-05T08:30:00Z
       
  • Quantitative analysis of macro steel fiber influence on crack geometry and
           water permeability of concrete
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Yining Ding, Dong Li, Yulin Zhang
      In this work, the water permeability of the cracked concrete has been investigated. Three types of cylindrical specimens with different fiber content were pre-cracked by the feedback controlled splitting test, and the specimens without any fiber reinforcement were also studied as reference. The water permeability of the specimens with different crack width was measured by hydraulic permeability test. The coordinate data of the crack surface was collected by the self designed data acquisition system, the total crack length and surface area of the samples were analyzed, the crack geometry (tortuosity and roughness) was evaluated quantitatively. A modified factor ξ was introduced to the Poiseuille law to verify the permeability of the cracked specimen. The results showed that with the addition of macro steel fibers, the deformability of the specimens was improved significantly and the crack width could be controlled. The coefficient of the water permeability of the specimens was declined by fiber addition, the modified Poiseuille law could be used to evaluate the water permeability of the cracked concrete, the modified factor ξ decreased with the increasing of fiber dosage. The crack tortuosity and surface roughness increased obviously with the addition of steel fiber.

      PubDate: 2018-02-05T08:30:00Z
       
  • Experimental investigation of composite pyramidal truss core sandwich
           panels with lightweight inserts
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Ge Qi, Li Ma
      Composite sandwich structures with lattice truss cores have both lightweight characteristics and multifunctional potential, which attract a large number of studies on topological optimization, manufacture process and performance evaluation in recent years. However, reliability study on the joint is an inevitable research subject for engineering application, and few studies on inserts within sandwich panels with lattice truss cores are published. In this paper, composite pyramidal truss core sandwich panels with lightweight metallic quadrangular-prism inserts are designed and fabricated. Pull-out and shear tests are carried out to investigate their load capability and failure behaviors, respectively. It is observed that, compared to the honeycomb panels, the present sandwich panels with quadrangular-prism inserts normally can obtain a similar level of pull-out strength but a higher level of shear load capabilities.

      PubDate: 2018-02-05T08:30:00Z
       
  • Damage detection in CFRP composite beams based on vibration analysis using
           proper orthogonal decomposition method with radial basis functions and
           cuckoo search algorithm
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Khatir Samir, Benaissa Brahim, Roberto Capozucca, Magd Abdel Wahab
      This paper presents a new fast approach for crack identification using vibration analysis based on model reduction using proper orthogonal decomposition method with radial basis function (POD-RBF). The method is formulated as an inverse problem for detecting the position, length and depth of crack in Carbon Fibre Reinforced Polymer (CFRP) composite structures, where Genetic and Cuckoo search algorithms are used to minimize the cost function based on numerical and experimental natural frequencies. The results show that the POD-RBF combined with Cuckoo search algorithm is an efficient and a feasible methodology of predicting the width, depth and position of double rectangular notches in CFRP beams. The stability of this technique is tested by introducing a white Gaussian noise in the frequencies data input. The results show that the proposed approach is stable when the noise level is lower than 6%.

      PubDate: 2018-02-05T08:30:00Z
       
  • Bending failure mechanism and flexural properties of GLARE laminates with
           different stacking sequences
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Huaguan Li, Yiwei Xu, Xiaoge Hua, Cheng Liu, Jie Tao
      Failure mechanisms of GLARE laminates with different structure were investigated by the combination of experiment and numerical simulation methods to predict the damage behaviors of GLARE in practical applications. In this study, bending properties were obtained under varied experiment parameters. Results indicated that the value of span-to-thickness ratio (L/h ratio), which could change the failure mode of laminates, had the most significant impact on bending properties. Effective bending failure occurred when L/h ratio ranged from 14 to 24. Moreover, the bending properties of GLARE laminates with different structures such as 3/2 (3 aluminum sheets and 2 glass/epoxy plies), 4/3, 5/4 and 6/5 were measured and compared. The data revealed that bending modulus decreased with structural expansion. However, the bending strength of unidirectional laminates increased with structural expansion, while the bending strength of cross-ply laminates decreased. SEM observation showed that the failure of GLARE laminates consisted of elastic stage, plastic stage, local fracture of fiber layer and delamination stage.

      PubDate: 2018-02-05T08:30:00Z
       
  • A hybrid discontinuous Galerkin semi-discrete finite element method for
           skewed and curved laminated beams/plates/shells based on Delta function
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Tianyu Li
      A hybrid discontinuous finite element method based on Delta function is developed for skewed and curved laminated beams/plates. Equal-order interpolations for displacement field and interface stress field are obtained without numerical oscillations. For the displacement field, the Consistent Orthogonal Basis Function Space is applied. For the interface stress field, the Delta function is used as basis functions. Two types of Delta functions are discussed. For the first type, the Delta function is defined uniformly on the interface. For the second type, the Delta function is defined on the Gauss points. It is observed that the numerical oscillation occurs in the first type for a large deformation analysis. For the second type, it is always numerical stable. The effect domain of the Delta function is discussed such that the stress on the interface is able to be calculated. The laminated plate and beam with clamped boundary conditions are studied. The interface shear stress is compared with ANSYS. Numerical oscillation is not observed for the second type Delta function with equal-order interpolations of displacement and interface stress. Skewed and curved laminated plates are also analyzed. The accuracy is still good for various angles between adjacent edges and various curvatures.

      PubDate: 2018-02-05T08:30:00Z
       
  • Ancient masonry arches and vaults strengthened with TRM, SRG and FRP
           composites: Numerical analyses
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Elisa Bertolesi, Gabriele Milani, Francesca Giulia Carozzi, Carlo Poggi
      The two arches and the three vaults experimentally described in Carozzi et al. (2017) are here analyzed with a novel robust FE lower bound limit analysis code, suitable to predict active failure mechanisms, lines of thrust and collapse loads in absence and presence of TRM, SRG and FRP reinforcement. The approach relies into a discretization into rigid-infinitely resistant quadrilateral elements for masonry, interfaces between contiguous elements exhibiting limited strength and perfectly bonded rigid-plastic trusses representing the reinforcement. For masonry, a No Tension Material NTM model can be adopted to compare with classic Heyman’s results, but also a limited compressive and tensile strength with a cohesive frictional behavior in shear may be accounted for in a relatively simple fashion, i.e. in principle with the possibility to model shear sliding and compression crushing. Debonding and delamination of the reinforcement are considered in a conventional way, assuming trusses with a limited tensile strength derived from either experimental data available or consolidated formulas from the literature. With the knowledge of the exact position of the hinges provided by limit analysis, 2D FE static analyses with non-linearity and softening concentrated exclusively on hinges are carried out, to simply extend the knowledge beyond collapse loads estimation towards a prediction of initial stiffness and ultimate displacements. In all cases, promising agreement with experiments is observed.

      PubDate: 2018-02-05T08:30:00Z
       
  • Flexural properties and morphology of microcellular-insert injection
           molded all-polypropylene composite foams
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Jian Wang, Dongjie Chen
      Single-polymer composite foams or all-polymer composite foams have been developed with further reduced weight, good interfacial adhesion and enhanced recyclability. All-polypropylene (PP) composite foams were prepared by the insert injection molding combined with microcellular injection molding. Flexural properties of the all-PP composite foams were reported and compared with solid PP, all-PP composites and PP foams. In comparison with solid PP, the 4.23% weight reduction, 16.52% increase of flexural strength and 20% increase of flexural modulus were achieved by the all-PP composite foams produced at the injection temperature of 220 °C and injection speed of 40 mm/s. Especially, the all-PP composite foams could have lower weight but higher flexural strength than the all-PP composites without foaming. The effect of injection temperature and injection speed on the flexural properties of all-PP composite foams was investigated to explore the optimum processing parameters for balancing good interfacial adhesion and weight reduction. Morphology properties were also investigated. The effect of processing conditions on the cell size and cell density of the all-PP composite foams was analyzed.

      PubDate: 2018-02-05T08:30:00Z
       
  • Numerical simulation on the deformation behaviors of bulk metallic glass
           composites under uniaxial tension and compression
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Wei Rao, Juan Zhang, Guozheng Kang, Peter K. Liaw
      The free volume model is firstly extended to describe the asymmetry of bulk metallic glass (BMG) presented under the uniaxial tensile and compressive deformations, and then the extended model is implemented into a finite element code as a user material subroutine (UMAT). Based on such a UMAT, a systematic numerical simulation is performed to investigate the deformation behaviors of BMG composites subjected to uniaxial tensile and compressive loadings. The von-Mises equivalent shear plastic strain is adopted to characterize the nucleation and propagation of shear bands in the BMG matrix here. The simulated uniaxial tensile overall stress–strain responses of the BMG composites containing different volume fractions, shapes, orientations and yielding stresses of toughening particles are compared with the compressive ones. It is shown that the initiation and propagation of shear bands in the BMG composites depend on the geometric features and yielding stresses of the toughening particles and present obviously different evolution features under the uniaxial tension and compression. The obtained results are very useful for designing and modeling the BMG composites.

      PubDate: 2018-02-05T08:30:00Z
       
  • Design-oriented crushing analysis of hexagonal honeycomb core under
           in-plane compression
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Zhen Li, Tao Wang, Yi Jiang, Liangmo Wang, Dan Liu
      The square honeycomb core is compressed quasi-statically and dynamically in order to investigate the mechanical properties of it. The plastic collapse stress under static compression is mathematically discussed by investigating the collapse mechanisms of cells from numerical simulations. Results show that the plastic collapse stress in the y direction is larger than that in the x direction under multi-cell condition, which agrees with the conclusion of numerical simulations. This difference is insensitive to the relative density within a specific range under quasi-static compression. However, it turns to be insignificant when the crushing velocity reaches or exceeds a critical velocity. A reverse method is proposed to estimate this critical velocity. For the equi-biaxial compression analysis, deformation process of the honeycomb is defined to three modes, and the deformation map is drawn. Compared with true stresses in both x and y directions in uniaxial compression, performances of them in equi-biaxial compression are reinforced. To represent the true stress in mathematical way, empirical formula for high velocity compression is derived. The energy absorption capacity is also enhanced, and the process is smoother around the stage of full densification than that under uniaxial compression.

      PubDate: 2018-02-05T08:30:00Z
       
  • Scattering of an acoustic wave by composite cylindrical shells: Influence
           of inner and outer layer thicknesses on the circumferential waves
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Said Agounad, El Houcein Aassif, Younes Khandouch, Dominique Décultot, Gérard Maze
      Acoustic scattering of a plane progressive wave from the composite cylindrical shell is investigated through the solution of the wave equation and boundary conditions of stresses and displacements. The investigated range of reduced frequency extends over 0.1 < k 1 a 1 < 200 ( k 1 is the wave number in a fluid medium surrounding the composite cylindrical shell and a 1 is the outer radius of the shell). The far field form function for two-layered stainless steel/polymer cylindrical shell is evaluated and examined. The achieved results are compared with those obtained in the case of one-layered cylindrical shells made of stainless steel or polymer. The investigation is carried out into the influence of the inner layer thickness (polymer) on the circumferential waves of the stainless steel/polymer composite cylindrical shell on the one hand and of the outer layer thickness (stainless steel) on the other hand. This influence is studied based on the evolution of the cutoff frequencies of the circumferential waves. A comparative analysis of the evolution of the cutoff frequencies of the one-layered and composite cylindrical shells is conducted. The estimation of the cutoff frequencies is done from plane of modal identification and two time-frequency planes, the spectrogram and the reassignment spectrogram. The results show that these planes are very useful to estimate the cutoff frequencies of the circumferential waves of the composite cylindrical shell. They can therefore be suggested as an alternative of the proper modes theory which is applicable in the case of homogeneous structures.

      PubDate: 2018-02-05T08:30:00Z
       
  • Form-finding method for multi-mode tensegrity structures using extended
           force density method by grouping elements
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Jianguo Cai, Xinyu Wang, Xiaowei Deng, Jian Feng
      Multistable tensegrity structures are an intriguing form of compliant prestressed structures. Due to their attractive properties, these structures are attractive for a wide range applications. This papers aims the form-finding problem of tensegrity structures with multiple equilibrium modes. An optimization method for form-finding of multi-mode tensegrity structures is applied and then an equivalent optimization problem of energy-based objective function with Lagrange multiplier, regarded as an extension of the original force density method, is established. After the structural elements are grouped according to the property of symmetry, the objective function is minimized by the gradient descent algorithm, and as a result, the lengths of cable as well as the nodal coordinates are obtained and different structural modes corresponding to different grouping conditions can be achieved. Finally, several different modes in different grouping conditions of a planar and a spatial tensegrity structure have been obtained to verify the efficiency of proposed method.

      PubDate: 2017-12-27T13:25:39Z
       
  • On the bulk modulus and natural frequency of fullerene and nanotube carbon
           structures obtained with a beam based method
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): M. Braun, J. Aranda-Ruiz, M. Rodríguez-Millán, J.A. Loya
      In this work, the natural frequency of vibration and Bulk modulus under hydrostatic pressure conditions of carbon nanotubes and fullerenes are investigated. For this purpose, three-dimensional finite element modelling is used in order to evaluate the vibration characteristics and radial stiffness for different nanotube and fullerene sizes. The atomistic method implemented in this work is based on the notion that nanotubes, or fullerenes, are geometrical frame-like structures where the primary bonds between two neighbouring atoms act like load-bearing beam members, whereas an individual atom acts as the joint of the related load-bearing system. The current numerical simulations results are compared with data reported by other authors, highlighting the greater simplicity and the lower computational cost of the model implemented in this work compared to other molecular dynamics models, maintaining accuracy in the results provided.

      PubDate: 2017-12-27T13:25:39Z
       
  • An enhanced spring-mass model for stiffness prediction in single-lap
           composite joints with considering assembly gap and gap shimming
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Yuxing Yang, Xueshu Liu, Yi-Qi Wang, Hang Gao, Yongjie Bao, Rupeng Li
      An enhanced spring-mass stiffness model was proposed, which was based on the supposition that the transverse shear stress under preload satisfies conical and spherical envelope, to predict the stiffness of the single-lap single-bolt composite joint with considering assembly gap and gap shimming. The validation experiments were conducted for different configurations. It shows that the analytical results were all in good agreement with the experimental results. Meanwhile, experimentally validated finite element model was used as an assistant validation in consideration of convenience and cost saving. The presented analytical model was then used for parameter studies, including gap size, gap radius and shim thickness. The major conclusions are: 1) as gap size increases 0.1 mm, the shear stiffness decreases about 1.1%; 2) the shear stiffness quickly becomes zero when the gap radius exceeds the boundary of the highly stressed portion; 3) shim thickness has much greater influence on the bolt stiffness than on the shear stiffness.

      PubDate: 2017-12-27T13:25:39Z
       
  • Investigation on the static and dynamic behaviors of non-pneumatic tires
           with honeycomb spokes
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Xiaochao Jin, Cheng Hou, Xueling Fan, Yongle Sun, Jinan Lv, Chunsheng Lu
      Non-pneumatic tires (NPTs) have wide application prospects due to their advantages of no run-flat, no need of air pressure maintenance, and low rolling resistance. In this paper, the static and dynamic behaviors of NPTs with different honeycomb spokes were investigated. Based on the static behavior of three types of NPTs with the same cell wall thickness of honeycomb or the same reference load carrying capacity, it is shown that the maximum stresses in spokes and tread of a NPT are much lower than that of traditional pneumatic tires, but its load carrying capacity is higher than the latter. In comparison with the dynamic behavior of three types of NPTs designed with the same load carrying capacity, it is found that the stress level in spokes and tread under dynamic loading are higher than that under static loading. The rolling resistance of NPTs with the smallest cell expanding angle is lowest, which is due to the lowest mass and smallest deformation of honeycomb spokes. Taking all these factors into account, it is suggested that an optimal NPT in applications is one with a small cell expanding angle and wall thickness.

      PubDate: 2017-12-27T13:25:39Z
       
  • Deterministic and probabilistic homogenization limits for particulate
           composites with nearly incompressible components
    • Abstract: Publication date: 1 March 2018
      Source:Composite Structures, Volume 187
      Author(s): Marcin Kamiński
      Conventional expressions for the homogenized tensor components relevant to the particulate composites consisting of two linear elastic constituents are modified here towards application of the incompressible component. This analysis is subdivided into two important engineering situations – a combination of the incompressible rubber particle with polymeric matrix and of the incompressible rubber matrix with carbon particles. This modification is done by limit transition with Poisson ratio to its upper physical limit and, further, by assuming that contrast parameter in-between Young moduli of both components tends to 0. Such an approach enables also for an analytical calculation of the sensitivity coefficients of effective elastic characteristics with respect to material or geometrical parameters of both composites, which can be a starting point for widely available gradient optimization techniques. Analytical formulas obtained in deterministic case are then used in uncertainty analysis where analytical formulas for the basic probabilistic moments and coefficients of the effective tensor are obtained while randomizing some material or geometrical parameters of the polymer matrix or carbon particles. Fundamental value of this approach is that the first two probabilistic moments, cross-correlations as well as probabilistic entropies are given by the exact analytical equations, so that they are not affected by statistical and non-statistical computer methods errors.

      PubDate: 2017-12-27T13:25:39Z
       
 
 
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